The present invention relates to an injection nozzle and a method for injection molding, particularly hot runner nozzles and nozzle tips.
Hot runner nozzles, especially nozzle tips, typically contain hang up areas in their flow channels that make color or material changing of the resin problematic. Purging the new color material through the nozzle tip can be time consuming and wasteful of the resin. Heretofore, the only completely effective way to make a clean color change is to dismantle and clean the nozzle assembly to remove all traces of the previous color resin. Clearly, this can be very time consuming and expensive and risks damaging the equipment if the color changes are frequently made.
U.S. Pat. Nos. 5,513,976 and 5,716,651 to McGrevy and 5,545,028 to Hume et al. show a nozzle tip with an element that induces a spiral flow pattern in order to promote improved color changing. U.S. Pat. No. 4,965,028 to Maus et al. and U.S. Pat. No. 4,711,602 to Baker show nozzle tips with mixing elements to improve the homogeneity of the resin flowing through the nozzle tips. However, these references are not entirely effective in overcoming the foregoing problem and promoting rapid color changing.
European Patent Application 0 546 554 to Gellert, published Jun. 16, 1993 shows a nozzle tip containing a central element with spiral vanes that promote a swirling motion to the flow of infeeding resin; however, this also is not entirely effective.
U.S. Pat. No. 4,501,550 to Nikkuni shows a nozzle tip having a central infeed channel which diverges into multiple channels to feed past a central tip in order to improve inconveniences of color or material exchange. However, this does not promote flushing of the melt bubble in the narrow annular space underneath the nozzle support flange.
It would be desirable to provide a simple and effective nozzle tip design that conveniently promotes flushing out of the previous material to make efficient material and color changes possible.
Accordingly, it is a principal object of the present invention to provide an improved injection molding nozzle and method for injection molding.
It is a further object of the present invention to provide an improved nozzle and method as aforesaid including a simple and effective nozzle tip design that simply and effectively promotes flushing out of the previous material to make efficient material and color changes possible.
Further objects and advantages of the present invention will appear hereinbelow.